The invention discloses an electric vehicle online charging system and a charging method. The system comprises a station device and an on-board device. A power-receiving pantograph controller and an on-board controller establish a wireless router. A vehicle controller of an electric vehicle and a charging pantograph controller exchange charging data through the wireless router. After determining that the charging conditions are satisfied, the vehicle controller makes the power-receiving pantograph controller lower the pantograph, so that a power-receiving pantograph can contact an electrode plate of the on-board device, and a charger can charge a battery system through the power-receiving pantograph and the electrode plate. According to the application, as the charger and the power-receiving pantograph are mounted on a ground station instead of in a vehicle, the charger and the power-receiving pantograph are not limited by the vehicle environment, and the usability and reliability of the online charging system are improved greatly.